10 - HSDPA Overview Rev A

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HSDPA Overview

Christofer LindheimerWRAN System Management

Top right corner for field-mark, customer or partner logotypes. See Best practice for example.

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Commercial in confidence HSDPA Overview 2005-09-272

Outline

HSDPA Principles HSDPA Channels and Bearers

– Power Setting of new channels

Capacity Management HS-DSCH Mobility Flow Control & Transport Questions and Answers


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What is High Speed Downlink Packet Access (HSDPA)

STANDARDIZED Integral part of WCDMA (3GPP Release 5)

REDUCED DELAY Reduced round trip time

CAPACITY 2 – 3 times improved system throughput

SPEED Higher bit rates: up to 14 Mbps

Smooth Upgrade Short time to market with existing sites


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Key Idea in HSDPA

Fast adaptation of transmission parameters to fast variations in radio conditions


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Shared Channel Transmission

HSDPA data channel is called HS-DSCH A set of radio resources dynamically shared among multiple users

– In the time domain– In the code domain

Channelization codes allocatedfor HS-DSCH transmission

8 codes (example)SF=16

SF=8

SF=4

SF=2

SF=1

User #1 User #2 User #3 User #4

TTI

Shared channelization

codes

User #5 (CODE MUX!)


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Short TTI (2 ms)

Reduced air-interface delay– Improved end-user performance– Required by TCP at high data rates

Increases benefit from other HS-DSCH features– Fast Link Adaptation– Fast hybrid ARQ with soft combining– Fast Channel-dependent Scheduling

10 ms20 ms40 ms

Earlier releases

2 msRel 5 (HS-DSCH)

2 ms


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Higher Order Modulation

16 QAM to be used when radio quality is good– E.g., close to base stations

Enables higher rates

16QAM

2 bits/symbol 4 bits/symbol

QPSK


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Fast Link Adaptation

Adjust transmission parameters to match instantaneous channel conditions

HS-DSCH: Rate control– Based on Quality reports from UE

(CQI= Channel Quality Indicator)– Adaptive coding rate– Adaptive modulation– Adapt on 2 ms TTI basis– Use “available power”

Compare– Release 99: Power control (constant

rate)

Good channelconditions

high data rate

Bad channelconditions

low data rate

rate adaptation


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Dynamic Power Allocation

Dedicated channels (power controlled)

Common channels

Power usage with dedicated channelst

Unused power

Power

HS-DSCH with dynamic power allocationt

Dedicated channels (power controlled)

Common channels

HS-DSCH (rate controlled)

Total cell power

Power

Total cell power

3GPP Release 99 3GPP Release 5


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Fast channel-dependent Scheduling

Scheduling = which UE to transmit to at a given time instant and at what rate

Basic idea: transmit at fading peaks– Tradeoff: fairness vs cell throughput

high data rate

low data rate

Time

#2#1 #2 #2#1 #1 #1

User 2

User 1

Scheduled user


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Fast channel-dependent Scheduling Examples of scheduling algorithms

– Round Robin (RR) Cyclically assign the channel to users Channel quality variance unexplored

– Proportional Fair (PF) Assign the channel to the user with the best relative

channel quality Improved cell throughput

– Max C/I Ratio Assign the channel to the user with the best channel

quality High system throughput but not fair


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P1,1

+

AC

K

Fast Hybrid ARQ with Soft Combining Rapid retransmissions of erroneous data

– Hybrid ARQ protocol terminated in RBS short RTT

– Soft combining in UE of multiple transmission attempts reduced error rates for RLC retransmissions

NA

CK

P1,2

P1,2

P2,1P1,1

P1,1 P2,1

NA

CK

P2,2

P2,2

AC

K

P3,1

AC

K

P2,1 P3,1

+

Transmitter

Receiver

RTT


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HSDPA Basic Principles

Shared Channel TransmissionDynamically shared in time & code

domain

Higher-order Modulation16QAM in complement to QPSK for

higher peak bit rates

2 ms

Short TTI (2 ms)Reduced round trip delay

Fast Hybrid ARQ with Soft Combining

Reduced round trip delay

Fast Radio Channel Dependent Scheduling

Scheduling of users on 2 ms time basis

Fast Link AdaptationData rate adapted to radio

conditions on 2 ms time basis

t

P

Dynamic Power AllocationEfficient power &

spectrum utilisation


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Node Impacts

RBS– HS-DSCH functionality

Scheduling, Link Adaptation, Hybrid ARQ…- …all implemented in RBS

RNC– Impact

Setup of HS-DSCH/HS-SCCH Setup of users on HS-DSCH Capacity Management, Cell change handling


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Outline





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HSDPA Channel Structure

RBS ARBS A

High-Speed Downlink Shared Channel – HS-DSCH-High-Speed Physical Downlink Shared Channel – HS-PDSCH : DL Data

HS-PDSCH

-High-Speed Shared Control Channel – HS-SCCH: Scheduling

HS-SCCH

Associated Dedicated Channel- A-DCH: Data in UL and control in DL

RBS BRBS BRBS B

A-DCH

-Multiplexed with High-Speed Dedicated Physical Control Channel: ACK/NACK + CQI

HS-DPCCH


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HS-DSCH and A-DCH

Shared channel:– HS-DSCH

Per HS-DSCH user:– A-DCH DL

3.4 kbps SRB (control signalling) Also needed for power controlling the UL

– A-DCH UL 64 (or 384) kbps DCH 3.4 kbps SRB (control signalling) High-Speed Dedicated Physical Control Channel

(HS-DPCCH)


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HS-DPCCH and HS-SCCH power

HS-DPCCH (UL)– ACK, NACK, CQI

Power offsets in relation to DPCCH Repetition of ACK, NACK, CQI based on performance

HS-SCCH (DL)– Fixed Power (relative to CPICH)


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UE capabilities

HS-DSCH category

Maximum number of HS-DSCH

codes received

Minimum inter-TTI interval

Maximum number of bits of an HS-DSCH

transport block received within

an HS- DSCH TTI

Total number of

soft channel bits

Modulation

Category 1 5 3 7298 19200 QPSK/16QAM Category 2 5 3 7298 28800 QPSK/16QAM Category 3 5 2 7298 28800 QPSK/16QAM Category 4 5 2 7298 38400 QPSK/16QAM Category 5 5 1 7298 57600 QPSK/16QAM Category 6 5 1 7298 67200 QPSK/16QAM Category 7 10 1 14411 115200 QPSK/16QAM Category 8 10 1 14411 134400 QPSK/16QAM Category 9 15 1 20251 172800 QPSK/16QAM Category 10 15 1 27952 172800 QPSK/16QAM Category 11 5 2 3630 14400 QPSK Category 12 5 1 3630 28800 QPSK


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HSDPA Services and RABs first HSDPA release

New RABs– PS Interactive

64/HS – PS Interactive

384/HS 16QAM is optional 1–5 HS-PDSCH

codes (configurable) All HS capable UEs

use HSDPA regardless of CN requested bit-rate

Theoretical max: BLER operating level 10 % will decrease values accordingly


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Outline





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Admission control

Load non

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Admission Granted

Admission Rejected

Admission thresholds varies depending on:

– Request class Guaranteed

- Conversational- Streaming

Non-guaranteed- Interactive- Background

– Request type Handover Non-handover


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Admission control

Power non

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A-D

CH

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hand

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A-D

CH

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Admission Granted

Admission RejectedCongestion threshold

Handover thresholdGuaranteed threshold

Non-guaranteed threshold

High load situations should still allow for access to remaining

power

MAX number of HS-DSCH users criterion


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Congestion control

Cell(s)

CongestionControl

AdmissionControl

“DL Congestion”Block ALL new requests

Start congestion resolve actions in the cellPeriodically:•Downswitch non-guaranteed users to Cell_FACH•Downswitch HS-users to idle state•Drop guaranteed usersMost resource-consuming users are targeted first


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RNC RNCIur

Iub Iub

Iu Iu

Associated Dedicated ChannelsHS-PDSCHHS-SCCH

HS-DPCCH

•Serving HS-DSCH Cell Selection (Intra and Inter-Frequency)

•No Soft/Softer HO for HS-DSCH

•Serving HS-DSCH Cell Change (Intra-RNC)

Iub

Overview of HSDPA Mobility


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Serving HS-DSCH Cell Change, -Mobility

The following events will trigger a serving HS-DSCH cell change

– A change of best cell within AS (event 1d)– SHO removal (event1b) – SHO replacement (event 1c)

RNC RNCIur

Iub Iub

Iu Iu

Associated Dedicated ChannelsHS-DSCHHS-SCCH

HS-DPCCH

Iub

No support for HS-DSCH over Iur


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Outline





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Purpose of Iub flow control

Pre-buffer data in RBS to allow fast scheduling

Avoid buffer overflow or empty buffers in RBS

Keep an appropriate amount of data buffered in RBS– Conflicting requirements

Keep the RBS priority queues short in order to avoid excessive RLC RTT

Keep enough data in queue to ensure throughput when scheduled

Ensure that the flow is within Iub Transport Network limits

SDU buffer

RNC

RBS

UE

RBS buffer

HARQ buffer

TN

(Scheduler)

RLC buffer

Iub flow control


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HSDPA enablers in the Transport

Iub solution optimized for efficient bandwidth utilization– With AAL2 Switching and UBR for HSDPA

New Best Effort AAL2 QoS class for handling HS traffic– Class C

AAL2 QoS separation between different traffic classes– A, B, C

User traffic Flow control for HSDPA

IMA for trunking gains– For >1.5Mbps HS bandwidth to a single user


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Iub Configuration with AAL2 Switching, UBR, IMA

T1

T1

3 MbpsClass B:

DCH best effort

Class C: HSDPA best effort

Class A:Strict QoS

Voice, Video, CS64, Common Channels

R99 PS Data

AAL2/CBR

B

A

AAL2/UBRC

ET-MC1 / MC41

HSDPA Peak rate of up to 2.2Mb/s

Slide titleIn CAPITALS

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Questions and Answers


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Documents

10 - HSDPA Overview Rev A